1. Field of the Invention
This invention relates to an encoder for measuring the amount of displacement resulting from rotation, movement or the like of an object to be measured. In particular, disclosed is an absolute type encoder which is capable of obtaining raw electrical data row due to the presence or absence of the reflected or transmitted light of a light beam entering a plurality of track portions provided on a code plate connected to an object to be measured, and finding the absolute position of the object to be measured therefrom.
2. Related Background Art
A photoelectric encoder has heretofore often been utilized as an apparatus for detecting the rotation, movement, position or the like of an object to be measured for detecting the amount and speed of rotation of a rotational mechanism.
FIG. 1 of the accompanying drawings is a schematic view showing an example of the absolute type encoder according to the prior art for measuring the position or the absolute amount of displacement of an object to be measured. In FIG. 1, the reference numeral 41 designates a rotational disc rotatable about a rotary shaft 40. A plurality of tracks are provided concentrically on the rotational disc 41 to generate binarized data in conformity with any angular position of the rotational disc 41. Optically binarized data, for example, a plurality of slits 42 each comprising a transmitting area and a non-transmitting area, are provided regularly on each track, and a particular data row is formed radially of the rotational disc 41. The reference numeral 43 denotes a fixed slit row which has a plurality of openings to selectively pass the light from the slits provided on each track and constitutes a slit row along the radial direction of the rotational disc 41. The reference numeral 44 designates light-projecting means having a plurality of light-projecting elements, and the reference numeral 45 denotes light-receiving means having a plurality of light-receiving elements. These two means are disposed with the rotational disc 41 and the fixed slit row 43 interposed therebetween so that each light-projecting element and each light-receiving element correspond to each opening of the fixed slit row 43 and each track of the rotational disc 41.
In the construction shown in FIG. 1, the light beam radiated from each light-projecting element of the light-projecting means 44 passes through the slits 42 and the fixed slits 43 to the light-receiving means 45. At this time, a row of data is read from a combination of the output signals of the light-receiving elements to thereby find the precise position of the rotational disc 41. The detected resolving power of the rotated position of the rotational disc 41 in such an apparatus becomes dependent on the number of tracks on the rotational disc 41.
That is, to enhance the detected resolving power, it is necessary to increase the number of tracks disposed on the rotational disc 41 and increase the combined elements.
However, an increase in the number of tracks leads to a greater diameter of the rotational disc 41 which in turn leads to the bulkiness of the entire apparatus and also to an increased number of signal output systems, which results in the problem that signal processing becomes complicated.